1. Field of the Invention
The invention relates to a method and apparatus for producing prints, especially multicolor prints, especially a proof, by means of thermal transfer.
2. Discussion of the Prior Art
The thermal transfer method has been known for years. In principle, a substrate, which may be the final substrate or an intermediate carrier, is brought into contact with a colored layer which has been applied to a carrier, and this colored layer is transferred to the substrate dot by dot, or in accordance with an image, under the action of heat.
By means of differently colored films, it is also possible for a number of colors to be applied one after another, and thus for a colored print to be produced. If the substrate is an intermediate carrier, the finished multicolored image is then transferred to the target substrate in a further step.
U.S. Pat. No. 5,164,742 describes a method in which the action of heat is achieved by means of laser radiation. This means that very small dots can be achieved. However, the method cited has the disadvantage that each film is laid on the substrate over its entire area. Achieving this without the inclusion of air is complicated. Furthermore, only materials which do not gas out during imaging can be used, since otherwise so-called tenting occurs, that is to say the material is lifted, contact between the adjacent regions of the film and the substrate is lost and it is no longer possible for the film to be imaged properly.
This restricts the usability both of the suitable materials and of the imaging arrangement, since during the (very brief) introduction of the energy in the normal case, not only is the material incipiently melted but also a plasma and gas are produced. In particular, limits are placed on the imaging speed, since the shorter the action time, the earlier the plasma is produced. Furthermore, laying a film on a substrate in an external drum imaging means is not possible unless additional fixing is provided.
German Patent DE 44 30 555 C1 discloses a method from another field of application, namely the production of offset printing forms.